


A Demons Heat is Hell

by DemonShippingQueen



Category: Ao no Exorcist | Blue Exorcist
Genre: M/M, Mpreg
Language: English
Status: In-Progress
Published: 2020-01-07
Updated: 2020-01-07
Packaged: 2021-02-27 13:35:47
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 4,935
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22157926
Author URL: https://archiveofourown.org/users/DemonShippingQueen/pseuds/DemonShippingQueen
Summary: Something is wrong with Rin that has everyone worried. Well almost everyone, but it doesn't look like Mephisto is going to tell them anything untill he feels like it. When the group sees Amaimon and Astaroth on the same day, they start demanding answers from the pink/anime loving demon. Though, can they handle what the answers will bring? M-perg. Adopted from daitenshi wings.
Relationships: Amaimon/Okumura Rin
Comments: 10
Kudos: 144





	1. Chapter 1

****Chapter 1** **

Rin Okumura was not having a very good day. He had been late for his normal school classes because he had over slept and missed breakfast. He didn't get to have lunch because he forgot to grab it when he was leaving. He couldn't find any of his friends or his brother to see if they could help him out. Fell asleep in his last class which made him late for Cram School and now he was starting to feel really hot. He felt like someone was poring fresh hot lava inside him. With each beat of his heart his insides grow hotter and hotter.

Rin got through his Cram School most of his classes fine until the heat got to be to much for him near his last class. He laid his head down on his desk when felt like it was started to spine. Shiemi, who was sitting next to him, looked over at him to see if he was all right. Her familiar, Nee, had jumped off of his spot on her head when Rin put his head down. She had thought, like everyone else in the room, that Rin was just being Rin. Though today she could tell he seemed to be not himself. He wasn't being goofy at all today and seemed to be in a bad mood. Then there was the fact that until now, Rin seemed to be really trying to pay attention in all his other classes. She watched Nee to see what her familiar was going to do before she said any thing.

Rin could hear the little steps of Shiemi's baby Greenman coming closer over to him. He turned his head a little so that he could see the little guy. He watched as Nee stopped right by his head and just sat down in front of him. It titled its head from side-to-side before nodding to itself. Rin was wondering what the Greenman was doing when suddenly he got a strong feeling to protect it. His hand shot out to wrapped around Nee, while his other hand flow up and cough a book that had been thrown at him by the teacher. Rin bared his fangs and let out a growl through his clinched teeth. He held the baby Greenman to his chest where he felt the little demon would be safe.

 **S** hiemi's, along with everyone else, eyes widen as she starred at Rin. Unlike everyone else they didn't see the whole thing like Shiemi, only that Rin had cough a book that was thrown at him without ever lifting his head. They hear the teacher call Rin name because everyone (but Shiemi) thought he was sleeping in class; though Rin hadn't hear the teacher and was just staring at the familiar. Shiemi saw the book heading over to Rin and Nee, she watch as the boy next to her eyes widened before they felled with anger. Nee chirped happy from where Rin was holding him. If the book hadn't been stopped Shiemi knew that Rin wouldn't be the only one hit by it. Nee had been to close to Rin’s head for it not to miss him.

"Nee!" Shiemi quickly reached out for her familiar. Nee looked over to her and let a loud happy chirp at his name and reached out one of his little arms for her.

Rin stopped glaring at his teacher and looked at Shiemi when she called out to her Greenman. Seeing her worried face calmed him down a little as he let the Greenman jump from his now open hand to hers.

"Thank you Rin. You okay Nee?" Shiemi asked once Nee was in her hands. She brought him up to her cheek to give him a hug.

"Nee nee," The demon answered back as he hugged her while rubbing his cheek on hers.

Rin turned back to the teacher letting out a low growl. "Next time look before you throw a damn book at someone asshole!" Rin got up from his seat and left the classroom, almost taking the door off the wall when he slammed it closed behind him.

 _'What the hell was that? Why did I do that? Better yet,_ _HOW_ _did I know something was going to hit us and catch it?'_ Rin asks himself as he walked down the hallway to get away from the classroom. He also noticed that, that weird heat went away too but was coming back with a vengeance now that he was claiming down.

He grabbed his stomach when the burning heat started to make him feel sick. His angry walking started to get slower and slower until he just stopped walking all together because of the quickly growing heat. Behind him he heard a door open and voices calling his name. The sounds of running feet reached his ears when he fell onto his hands and knees. The voices had reached him and someone was put their hand on his back asking him what was wrong.

"What's going on? What's happening to me?" Rin weakly asked to anyone who might be able to hear him. He fell to the ground on his right side as the heat turned in to pain through out his whole body. He screamed to the high heavens as his body filled was a none stop growing pain and his insides began to burn with the hottest flames in the two worlds. That was all he know when the world around him turned to darkness. Some of the heat and pain following him.

Rin’s friends and brother were all gathered around him. They felt helpless as they watched him pass out from what ever was causing him pain. Everyone jump as they heard a voice beside them.

"Oh dear, what seems to be going on here?"

**~A/N:**

****As a New Years gift to you all I am up loading all the stories and the chapters that I've adopted and have fully finished fixing.** **Let me know how you like this chapter. On to the next chapter.** See you next time!**


	2. Chapter 2

****Chapter 2** **

Mephisto sat is his chair behind his desk with a smile on his face as he looked at the group of Cram School kids sitting in front of his desk. They had followed him to his office when he had picked up Rin off the grown of the Cram School halls. A few of them asked him questions on their way to his office but he just told them to wait before he would answer any of them. He took Rin and put him in the bedroom he had in his office for when he couldn't make it home. His little brother was sound asleep even though it was not a peaceful one. Now he sat that his desk and waited to see who would be the first one to get tired of him just staring at them. He didn't have to wait to long as his other little brother finally stood up from his seat and yelled at him.

"What's wrong with my brother!" Yukio glared angry at the man in front of him.

"No need to shout Mr Okumura, I'll be happy to tell you what is going one with our lovely Rin." Mephisto said with a smile on his face. "What Rin is going through is very normal for demons his age. Rin has reached the age of 16 this year and will reach the age of 17 next year. He will be find."

"That doesn't answer anything at all!" Bon growled out through his teeth.

"I'm afraid that is all the time I have right now. I believe you all have homework to do and you, Yukio, have some jobs to do." Mephisto said as if he hadn't heard Bon at all.

Seeing that he wasn't going to say anything as he looked away from them and down at the paperwork on his desk; the group left the room. Yukio looked back before he left and giving the clown one last glaring before he left. When the door closed Mephisto got up and walked into the room Rin was in. Standing by the bed he looked down at his little brother with a sad smile.

"You are going to be in for quit a ride when you wake up little Rin. I just hope you get the one who will be right for you and you'll like them." He ran a gloved hand through the boys black hair. "Not all get as lucky I did."

****(A few days later)** **

The gang was heading over to their spot to eat some lunch when some one walked over to them. The others had never seen this person before but Yukio seemed to know them. He put on a black face as he put himself between the new comer and the group. Bon thought it was kind of weird that his teacher would do at because of what looked like a normal student. However, as the student got closer he saw why Yukio was in a defense of pose. The guy was possessed and was swarming with Coal Tars. They had tightly curled ram horns coming out the side of their head with black pointed nails, and a long black tail whipping behind him that reminded them of Rin's. The student also had white gray hair and three piercings on his face.

"Hey there little Okumura. Just the person I was looking for." The student smirked showing off his sharp fangs. "Wheres your big brother? Doing well I hope, hehehe."

"What are you doing in Shiratori's body again. You where exorcised twice from it already." Yukio glared at the boy as he placed a hands on one of his guns.

"Looks like this body likes me better then its owner. It even feels good; a nice fit." Shiratori's tail swayed back and forth behind him calmly. "I already said what I wanted. Are your ears going bad?"

"Yukio, who is that?" Shiemi asked as she stepped a little closer to him.

"Stay back Shiemi. That bodies name is Reiji Shiratori but the one who is in it right now is the Demon King Astaroth."

"Nice to meet all of you." Astaroth gave them a dramatic bow. "You'll be seeing me around a lot more." He turned back to Yukio. "It seems like your brother isn't here. No matter I'll be seeing him soon anyway." With that he turned and left them with a wave as he walked away.

"What was that all about?"Izumo asked as they watched the demon walk away.

"I don't know but I think Mr. Pheles does." Yukio said as he started to lead the group to the anime loving demon.

Yukio could feel his worry for his brother growing. They hadn't been able to see Rin since he was taken away after his fall; now Astaroth finds away to get back into Shiratori's body and get on school grounds? Mephisto was going to tell them what was going on or he would shot the man himself. As they got closer to the main building they where stopped by a voice behind them.

"Hello again little brother. Are you going to go see big brother?"

The group turned around to see The Demon King of Earth standing behind them holding his Goblin, Behemoth, in his arms. The groups eyes widen at him as they quickly grabbed the weapons.

‘First Astaroth now Amaimon; what was going on?’ The group all though.

"I-i thought you died!" Shima said trying not to show that he was shaking.

"No, I just lost my body for a while. I'm glade I got it back in time though. I been waiting a long time for it to finally start." Amaimon started to say as he pet Behemoth. "Maybe it well finally be my time. I haven't been able to fine anyone I like." He said; though it sounded like he was talking to himself more then the humans in front of him.

A gust of wind came out of no where form behind the group bring their sent over to the Earth King. He sniffed the air and the group watched as his eyes widen before they turned to slits like he was mad. Shima and Konekomaru moved a little closer to Bon and Yukio as they remembered the last time he had that look on his face.

"Brother Astaroth is here as well." Behemoth started to growl. "I will take you to brother." It wasn't a request as he walked over to them and counted to walk past them.

The group share a look at each other before following after demon. Whether being lead by a demon or not they were all going to the same place in the end anyway.

****(In side Mephisto's office)** **

Mephisto looked up form his paperwork when his office doors open and he saw Amaimon come in followed shorty by Yukio and his friends. The group of humans had a mix of worry and anger looks on their faces, while Amaimon looked completely pissed about something. Letting out a sigh he put his work away and summoned some snacks and drinks. When he saw Amaimon not even look at the food he sat up a little straighter in his seat. Grabbing himself a cup of tea he looked at the odd group in front of him.

"What brings you all here and what has gotten into Amaimon for him to be like this?" He asked them.

"Astaroth is here brother." Was all Amaimon said as he glared out the big window behind Mephisto's desk.

"Ah, I see." He turned to look at the humans. "Is that why you are here as well?" He asked them.

"It's park of it, yes, but the main reason is we want to know is going on." Yukio answered.

Amaiomon walked over to the floor to ceiling windows behind his deck and crouched down in front of it. "Not telling people thinks again brother?" His eyes roamed around the ground below him as he began to bit one of his thumb nails.

Mephisto just rolled his eyes at his brother before he spoke to the group. "What is going on right now is mating season for some demons, which is the answer to you question." He took a sip of his tea before his continued. "And Rin is of age to finally join."

"What! What do you mean?" Bon asked. They haven't gone over about demons mating seasons in class yet.

"Well you see Mr Suguro all demons have a mating season and some, like Rin, got through what you call a heat. The beginning of the first heat is very painful and the demon goes into a coma like sleep for a full week. Rin has been asleep for 4 days and still has 3 more to go before he wakes up. Now demons go into their mating season at different times; the way you can tell when they will go into their heat is by knowing when they were born. Rin was born in Winter so his season is Summer, and since Summer has just started so has his first heat." He stopped to take another sip of his tea and turned to look at the door that lead to Rin. "When the demon sleeps it needs to be guarded by a strong demon to keep them from others; luckily the sleep only happens once. This is why I haven't let anyone one see him since I first took him."

"So, Astaroth found a way onto the grounds so that he could mate with Rin?" Izumo asked. "But isn't Astaroth like one of his older brothers? Isn't he not aloud to do that?"

"Yes and No, Miss Kamiki. Yes, they are bothers through Satan but for demons that doesn't really matter most of the time. Astaroth wants a strong mate, if that means it well be one of his own bothers so be it. Not all of us are like that but there are still some that are."

"Then shouldn't we be worried about you too?" She asked again.

Mephisto smirked at that, the girl had a sharp mind on her. "I don't think like my brother and I have already been mated. Most demons that guard the beginners are normally already mated demons or their parents."

"Um, what about A-amaimon?" Shiemi asked in a bit a shy voice.

Mephisto turned to look at his brother. "Well, are you going to answer or shall I?"

Amaimon didn't turned form the window but he did stop his nail biting. "I don't care either way. However, not many of my other bothers are like Rin. I have looked for a mate but none seem to feel like the right one."

"But your going to go after Rin like Astaroth?" Shiemi asked him.

"Yes, Rin feels different from the other demons who I have encountered gone into heat in the past. I would like to win Rin and mate him." Amaimon went back to biting his nail.

"Win Rin?" Shima asked Mephisto.

"Yes, other demons fight each other to see who will get to the demon in heat." The older demon answered.

"Your make it sound like Rin is a female cat that the other males are trying to get at." Konekomaru said with a little laugh.

"He is," Came Amaimon's voice.

"What?" The little monk asked.

"Rin is a cat; his is also in heat. Though he won't acted like a cat in heat until he loses a fight with the one who becomes his mate." Amaimon answered back as he got up and walked over to the others. Finding an empty seat he sat down and began to eat some of the sacks.

"If you're after Rin too how come you are this close to him?" Izumo asked the green hair demon.

"I'm no mach for my brother. He know that Rin is safe from me as long as he is between me and the door leading to Rin." With that he began to stuff his face with food.

Yukio had a dark blank look on his face at what Amaimon had said about Rin. "Mr. Pheles, why does the first heat hurt some demons and not others."

Mephisto gave the boy a small smile. "It is because their body is getting ready for when the demon finds a mate. The body changes form the inside to make room for some new things that grow in the week they are asleep."

"Why would it do that? What will the new stuff do?" Shiemi asked.

"It's to help Rin carry young isn't." Yukio said with an empty voice.

"Yes, that's right. Even male demon can carry young, though there are not many of them." Mephisto answered. "Whoever Rin mates with he well bare them one or more children."

"One or more? Why's that?" Came Shima's voice.

"It depends on what animal the demon can turn into. Amaimon is a hamster, I'm a dog, and you can tell by how Rin acts that he is cat. Now, there is a limit for even demon about how many they can give birth to. Lucky, how many babies can be born depends on the mother’s demon animal and not the father’s demon in Rin case." Mephisto turned to look out at the window behind him. "Now this part is very important that you all should know. There while be lower and higher demon that while come after all of you. You are seen as part of Rin's human family and they will try to beat you in a fight to show you that they will strong protectors for Rin. It will test all of you on your strength as a fighter and as a team."

He turned his head to look at them again. "And it won't be just demons come after Rin; human will to. Once Rin wakes up he will let off a sent that will bringing the maybe mates to him. Astaroth most likely was told by one of his Coal Tars about Rin since they fly around everywhere. Amaimon was coming to see me and that's how he found out. I won't leave Rins side until Rin's mate comes to fight him. I well know if they didn't beat you in a fight first before they reached me so no need to worry about that." He got up from his deck and started to walk over to the door that lead to Rin's room. "All of this most be a lot to take in, so I'll leave you to let is all sink in your heads. You know where the door is, and Amaimon you better be gone by the time I come back." With that he went into Rin's room and left them to their thought.

Amaimon grabbed a few snakes before heading to the office's door. "I'll be seeing you all later then." He said as he left with Behemoth behind him.

Everyone one else soon left as well and headed to there dorm rooms. They had a lot the think about and to get ready for in the next three day.

**~A/N:**

**To anyone is wonder why the humans are not questioning why Amaimon is calling Mephisto brother, it because they think that Amaimon just see him as a brother since he is stronger then him. They all know that Mephisto is a powerful demon, just not that he is a Demon King as while. Hope you like the chapter, let me know what you like of it. See you guys next time!**


	3. Chapter 3

****Chapter 3** **

****(4 Day Jump)** **

Rin's body felt really hot as he laid in bed. He had just woken up yesterday and Mephisto had told him what was happening to him like he had with his friends. It was a lot to take in but he didn't really mind for some reason. He knew he should be freaking out like his brother and friends must like have; but he didn't feel like anything was wrong. Mephisto told him that he would be taking care of him until his maybe mate came to fight him. So far nothing had happened and the purple haired demon had told him no demons have showed up to fight yet. Some had been seen outside the school but none had found a way in yet. The two Demon Kings have been keeping quiet; those Astaroth has been seen watching Rin's friends when they are not in Cram School.

The door to his room flew open and he saw Mephisto walking in holding his lunch for the day. Rin didn't know where the food came from or who was making it but it was good and made him feel better after eating it. Mephisto would even eat with him so that he wouldn't feel lonely when he was awake. He smiled at the older demon as he put the food down on the nightstand beside the bed.

"Good afternoon Rin. How was your nap?", Mephisto asked as he helped Rin sit up against the headboard.

"It was okay. The pain wasn't too bad this time; I'm just really hot." Rin responded as he rubbed his still sleepy eyes.

Mephisto let out a small chuckle. "Yes, that heat is going to stay with you until you have to fight. It will come back when you lose but you will like the feeling it brings with it."

Rin blushed a little at that, though it was hard to see it because of the fever.

"I brought someone to see you today, well two someones actually. The other one is a tag-a-long that wouldn't go away no matter what I did." Mephisto said as he gave Rin his lunch. "But you don't get to see them until you finish your lunch."

"Yes mother hen," Rin said as he rolled eyes and began to eat.

Mephisto smiled as he watched Rin eat. Like he had said before, he was a mated demon but he was not like Rin. He could not have young but he and his mate would have been good parents if he could. He saw Rin as his puppy, not his little brother, ever since his heat began. It was out of character for him to act this way, but Rin wasn't saying anything as he showed this other half of himself around the younger demon. Mephisto's only wish was that his mate was here to help and share this with him.

"Hey are you okay?" He heard Rin ask, his voice breaking threw Mephisto's thoughts. "You look sad all of a sudden."

"Yes, I'm alright Rin. Just thinking about someone I'm missing is all." He told him giving a little smile.

Rin just gave him a nod before going back to his food. Mephisto watched him for a little longer before joining him.

When they were done Mephisto took the plates and left the room. When he came back he poked his head in through the door frame with a smile on his face.

"Ready to see who has come to see you Rin?" The younger demon nodded slowly in reply.

Mephisto opened the door wider and a black blur streamed into the room.

 _"RIN!”_ A voice rang through the teen's head. _"I missed you! I'm sorry I wasn't with you when your heat started. I was chasing a demon that was hanging out around our home that was bugging me!"_

Rin chuckled has he hugged his familiar close to him. "It's okay Kuro, I understand. You were just keeping our home safe from the bad guys." Kuro began to purr at Rin's words. "I'm just glad to see you."

Rin felt something jump on to the bed and he looked over to see what it was. What he saw made his eyes widen with surprise. He held Kuro a little tighter to him as he stared at the newcomer.

"Behemoth," Rin said in a shy voice.

"Oh, you remember his name?" Mephisto's voice said from beside him. "He is Kuro's tag-a-long that I had mentioned."

Rin's eyes never left the Goblin as it moved to sit next to his legs. "Why is he here? He is Amaimon's familiar."

"Fear not, he is safe to be around you. Familiars know better than to try and steal their master's possible mates." Mephisto told him as he rested his hand on Rin's head. "He is here to help guard you and keep you safe. Some demons will send their familiars to show that are serious about wanting to be your mate. Others do it so that they can spy on you so they know when it'd a good time to sneak in and steal the demon in heat from it's guards."

"How do you know which is which in this instance?" Rin asked still not looking away from the green demon.

"You can sometimes tell by how the Familiar acts. If it's the first reason they stay close to their masters possible mate; like Behemoth is doing. If it is the other then they stay far way from the possible mate of their master." The older demon answered. "Though even then you could still be tricked. That is why when I leave I'll take him with me. Kuro will be able to stay with you though."

Rin finally looked away from the Goblin and up at the purple demon. "Really! He can stay with me?!"

"Yes, he will be your second guard and he will fight your possible mate as well." Mephisto nodded down at Rin. "He'll be with you when I am not. Now I think you should go back to sleep."

Rin yawned as he nodded his head. Kuro jumped out of Rin's arms and landed onto the pillow next to Rin's. Mephisto helped the younger demon lay down and grabbed Behemoth off the bed. Rin's eyes closed as soon as his head hit the pillow and was asleep a second after that.

Kuro looked over at the older demon once he lied down next to Rin's head. _"I'll watch over him with my life. You can trust me sir."_

"I know I can Kuro," Mephisto nodded to the two tail cat before he turned and left the room with the Goblin in hand. Once the door closed behind them Mephisto looked down at the demon in his arms. "You will guard Rin on this side of the door, got it."

Behemoth nodded with his whole body as he jumped out of his master's older brother's arms and stood in front of the door. Nodding back to the smaller demon, he walked over to his desk and sat down. Summoning a cup of tea for himself he let out a quite sigh as his eyes turned to his office's main doors. A minute later he heard a knock and they began to open.

"Hello there it's been a while hasn't it?" Mephisto said to the newcomer. "To what do I own the pleasure of this little get together?"

"You know why I'm here."

**~A/N:**

**And there we go, the last of the old chapters is has been fixed. All the chapter for this storied after this one will be new. **I’ll be using the notes** **I** **was give** **n** **with th** **is** **story along with some of my own ideas.** I can’t wait to truly start this this story! Let me know what you think of this chapter! See you guy next time!**


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